1. Field of the Invention
The present invention relates to an image reading apparatus including an imaging unit that forms an image of light from a document, and a image sensor that receives the light from the document via the imaging unit, and a method for assembling the image reading apparatus.
2. Description of the Related Art
Conventionally, there is an image reading apparatus including an optical unit as illustrated in FIG. 10. The optical unit uses an imaging unit to form an image of light from the document on a solid-state image sensor, and thus generates image data of the document.
In general, when the image reading apparatus is assembled, optical adjustment is performed as follows.
Referring to FIG. 10, a solid-state image sensor 100 is mounted on a solid-state image sensor substrate 101. The solid-state image sensor substrate 101, on which the solid-state image sensor 100 has been mounted, is fixed to a substrate holding member 102. An imaging unit 103 is fixed to an optical unit frame 104. After the optical adjustment is performed, the substrate holding member 102 is fixed to solid-state imaging unit holding members 106a and 106b, which are fixed to the optical unit frame 104. The position of the solid-state image sensor 100 with respect to the imaging unit 103 is adjusted in performing the optical adjustment.
More specifically, the substrate holding member 102 is temporarily held by an adjustment tool (not illustrated). A gap of approximately 1 mm is then formed between the substrate holding member 102 temporarily held by the adjustment tool and the solid-state imaging unit holding members 106a and 106b. The adjustment tool is then used to move the substrate holding member 102, to which the solid-state image sensor 100 is fixed via the solid-state image sensor substrate 101. The position of the solid-state image sensor 100 in X, Y, and θ directions is thus adjusted to adjust the focus on the solid-state image sensor 100.
Adhesives are then injected to and fixated in the gap between the substrate holding member 102 and the solid-state imaging unit holding members 106a and 106b at fixed portions 107a, 107b, 107c, and 107d in the adjusted position. As a result, the substrate holding member 102 is fixed to the optical unit frame 104. In other words, the solid-state image sensor 100 and the imaging unit 103 are fixed to the optical frame unit in a focus-adjusted state. Adhesives, such as a naturally curable adhesive, an ultraviolet curable adhesive, and an instant adhesive, are used.
In recent years, the adhesive is automatically applied, and efficiency is thus improved. However, since the adhesive is made of a material such as acrylic resin and epoxy resin, there is a lack of strength.
Further, solder may be used as a fixing member instead of the adhesive. The fixing strength of the solder is sufficient. However, soldering needs a skilled worker. For example, if a soldering iron is pressed on the substrate holding member 102 while soldering, the position of the substrate holding member, which is only temporarily fixed by the adjustment tool, becomes displaced. Fixing using the solder is thus inefficient.
Furthermore, when the adhesive hardens, volume contraction occurs, so that a relative distance between the solid-state image sensor 100 and the imaging unit 103 is changed. As a result, focus variation occurs before and after curing, and image degradation is generated. In recent years, an increase in the pixel number of the solid-state image sensor has made the solid state image sensor sensitive to changes in the focusing. As a result, the defocusing amount caused by the change in the volume when the adhesive hardens is not ignorable.